1. Field
The presently disclosed subject matter relates to semiconductor light-emitting devices including an LED chip and to a manufacturing method for the same, and more particularly to reliable semiconductor light-emitting devices including a silicon resin for encapsulating the LED chip and to the manufacturing method for these devices.
2. Description of the Related Art
Various semiconductor light-emitting devices including an LED chip have been used for general lighting in recent years. One reason is that an LED chip may be a favorable light source with respect to energy savings and environmental concerns. In addition, semiconductor light-emitting devices including an LED chip can emit variously-colored light while the structure thereof can be thin and small in size. High power LED chips have been developed and have been used as a light source in keeping the above trend.
However, while high power LED chips have been used as a light source for light-emitting devices, an epoxy resin that has been generally used as an encapsulating resin for LEDs has become difficult to use for semiconductor light-emitting devices, especially for devices that require high reliability. This is sometimes due to stress caused by a difference of thermal expansion coefficients between the material for mounting the LED chip and the encapsulating resin that is composed of epoxy. In some cases, a semiconductor light-emitting device that includes the epoxy resin may be damaged by the above-referenced stress. In addition, an epoxy resin may deteriorate in terms of quality and function thereof due to ultraviolet rays emitted from an LED chip, especially from the high power LED chip that can emit a light of high intensity.
Thus, while high-power LED chips become more prevalently used as a light source for a semiconductor light-emitting device, a soft silicon resin has been more frequently employed as an encapsulating resin in these devices. A characteristic of the soft silicon resin is that it may not be damaged by the above-described stress and may not deteriorate in quality due to ultraviolet rays. A soft silicon resin can generally resolve or reduce the problems caused by the ultraviolet rays and the stress. However, certain other problems or concerns are present when using a soft silicon resin, such as the characteristic that dirt and dust may easily attach to a surface thereof during the manufacturing process for the light-emitting device. Dirt and dust and other debris are attracted to the silicon resin because the surface thereof might be tacky.
A conventional light-emitting device that may resolve the above-described problems, for example, is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2007-036030). According to Patent Document No. 1, and as shown in FIG. 6, a pair of lead frames 23a, 23b is insert-formed in a casing 21 that includes a cavity 22 for encapsulating an LED chip 24 with encapsulating resins described later. The pair of lead frames 23a, 23b is depicted on a bottom surface of the cavity 22.
The LED chip 24 is mounted on the lead frame 23a via a conductive material and has one electrode thereof that is electrically connected to the lead frame 23a via one bonding wire 25a. The other electrode of the LED chip 24 is electrically connected to the lead frame 23b via the other bonding wire 25b. A first silicon resin 26a including a phosphor 28 is disposed in the cavity 22 so as to encapsulate the LED chip 24.
The phosphor 28 can absorb light emitted from the LED chip 24 and can convert the light into a different wavelength of light as compared to that of the light emitted directly from the LED chip 24. Therefore, the light-emitting device including the LED chip 24 may emit variously-colored light according to the type, quality, kind, etc., of phosphor 28 located within the resin 26a. The first silicon resin 26a including the phosphor 28 may also protect the LED chip 24 from problems caused by dust, moisture, etc.
In this case, dirt and dust may attach to a surface of the first silicon resin 26a. Accordingly, the surface of the first silicon resin 26a is covered by a second silicon resin 26b that is configured with a hard silicon resin having a higher hardness as compared to the first silicon resin 26a. Thus, the second silicon resin 26b having a high hardness can prevent dirt and dust from attaching to a surface thereof, and therefore the light-emitting device can operate reliably and maintain predetermined optical characteristics.
However, the above-described light-emitting device requires a process for covering the surface of the first silicon resin 26a with the second silicon resin 26b during manufacture. In addition, the light-emitting device requires both a process for at least partly solidifying the first silicon resin 26a before covering it with the second silicon resin 26b and a process for solidifying the second silicon resin 26b. Thus, a manufacturing method for the light-emitting device may include certain problems or concerns, such as increased lead time for manufacturing the device as compared to that for manufacturing a conventional light-emitting device.
In addition, the second silicon resin 26b may be difficult to form in a thin and uniform layer in a short time with a simple manufacturing machine. Thus, the light-emitting device may be difficult to form in a thin manner while accomplishing predetermined optical characteristics in line with the trend of providing thinner devices. The conventional device may also include variability in terms of optical characteristics from product to product if a thickness of the second silicon resin 26b cannot be made uniform in the overcoat and solidifying processes.
On the other hand, an inventor of the disclosed subject matter discovered that a microparticle such as silicon dioxide and the like can be useful as a luminescent material as disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP2006-143861). A manufacturing method for the microparticle is also disclosed in detail in Patent Document No. 2.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.
1. Patent Document No. 1: Japanese Patent Application Laid Open JP2007-036030
2. Patent Document No. 2: Japanese Patent Application Laid Open JP2006-143861
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include semiconductor light-emitting devices and associated manufacturing methods that do not cause and/or are designed to prevent some of the above-described problems, concerns, and characteristics related to a thin and uniform overcoat and the manufacturing lead time, etc. The disclosed subject matter can also include a light-emitting device that is configured to decrease optical variability caused by differences between a light-emitting color emitted from the optical axis thereof and a light-emitting color emitted in an inclined direction from the optical axis, and can reduce or change other associated problems, features, and characteristics of the conventional devices and methods.